It has a rising value because you can convert it back into dollars. It's also worth pointing out that same banking BS protects not only often protects their business but their customers as well... are there bitcoin "banking" services that provide that same level of service to businesses? With that in mind, are there any serious businesses that exclusively accept bitcoins?
If it has a rising value then it's in your interest to hold at least some of it unless you think it's about to crash.
If you are a merchant then the easiest way to start holding it is to start accepting payments with it, which is easy enough to do especially if there are enough people holding it already.
At that point it has value not just because you can convert it , but because you can buy stuff with it.
